Hammermills for shredding scrap materials such as automobiles shred or fragment the scrap materials using a rotor assembly with a plurality of impact hammers mounted thereon. The hammers are generally mounted to the rotors using pins and swing freely on the pins as the rotor rotates and the hammers contact scrap materials. The hammers are subjected to extreme wear conditions, and must often be replaced at significant cost. Many replacement methods and hammer designs have been employed in an effort to reduce the frequency at which the hammers must be replaced and the cost to do so.
One common practice for prolonging the life of the hammers is the use of two-piece hammers or hammers with replaceable tips. As shown, for example, in U.S. Pat. No. 3,829,032 to Schrimper, U.S. Pat. No. 4,000,889 to Whitney, and U.S. Pat. No. 4,202,504 to Cameron, a tip is mounted on the end of the hammer. As the hammer is in use, the tip is subjected to the most wear. The tips are easier and less expensive to replace than the entire hammer. Another method for dealing with hammer wear is to include a series of pin holes along the hammer. The pin hole nearest the impact end of the hammer would be used first, and then as the impact end of the hammer became worn, the next pin hole would be used. This practice prolongs the life of the hammer, but movement of the hammer pins from one pin hole to another is still costly and inefficient. One response to that problem is shown in U.S. Pat. No. 5,381,975 to Chon et al. (the “Chon et al. patent”), which discloses a hammer that allows for changing pin holes without removal of the hammer pin. Instead of discrete pin holes along the length of the hammer, the hammer in the Chon et al. patent includes an elliptical slot and a removable plug. To move the hammer to a new pin location when worn, the plug is removed, the hammer is moved into its new location, and the plug is replaced to hold the hammer in place.
Although existing methods for extending the life of the hammers have certain benefits and advantages, existing methods also have limitations. In particular, the common methods are not very effective for heavy industrial shredding applications, such as the shredding of scrap automobiles, trucks and the like. Such applications require much larger hammermills and hammers, which makes replacement of any parts even more costly and inefficient, and any additional parts used in connection with mounting the hammers to the hammermill rotors must be especially robust.
The present invention relates to improvements over the hammers and hammer assemblies described above, and to solutions to the problems raised or not solved thereby.